feat(v4.0.0): the host node's stacks are 32 deep (D-17)

With the stacks counted and guarded (D-16) their size is a parameter of
the node.  The host node, which runs the interpreter and the compiler
under the user's programme, gets 32 values and 32 return entries; a mesh
node keeps the F18's 10 and 9.  Nothing else about the mechanism or any
word's definition changes.

- stack.h: V4_DATA_RING and V4_RET_RING are build parameters; the
  Makefile sets them for the host-node tests.
- tests/test_host_quit.c no longer assumes a size: it fills the stacks to
  whatever they are, and takes every exit with the return stack full.
- Measured on the host node now: 28 values on a line, 29 waiting between
  lines, words 31 deep from the prompt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/Makefile

@@ -40,8 +40,14 @@ BINDIR  := $(HERE)/build
 # dictionary and the text being compiled (JUSTIFICATION.md section 9), which
 # do not fit 1024 words.  Tests named test_host_*.c are therefore built with a
 # host node of HOST_WORDS words; every other test keeps the mesh-node size.
-HOST_WORDS := 16384
-node_size = $(if $(findstring /test_host_,$(1)),-DV4_NODE_WORDS=$(HOST_WORDS))
+#
+# The host node's stacks are deeper too (DECOMPOSITION.md D-17): 32 values and
+# 32 return entries, where a mesh node has the F18's 10 and 9.  The stack is
+# its top registers and a ring; the ring sizes are what is set here.
+HOST_WORDS     := 16384
+HOST_DATA_RING := 30
+HOST_RET_RING  := 31
+node_size = $(if $(findstring /test_host_,$(1)),-DV4_NODE_WORDS=$(HOST_WORDS) -DV4_DATA_RING=$(HOST_DATA_RING) -DV4_RET_RING=$(HOST_RET_RING))
 
 # The capsule sources: definitions as text (include/v4/text.h), which tests
 # assemble onto a node.  The directory is passed to the tests so that they